Diamond coated tool

ABSTRACT

The present invention provides a diamond coated tool which is resistant to exfoliation at an interface between a base material and a diamond layer. The diamond coated tool of the present invention is a diamond coated tool including a base material and a diamond layer coating a surface of the base material, and characterized in that the surface of the base material has an arithmetic average roughness Ra of not less than 0.1 μm and not more than 10 μm and an average length of roughness profile elements RSm of not less than 1 μm and not more than 100 μm, and that the diamond layer has a plurality of cavities extending from a portion bordering on the base material in a crystal growth direction.

TECHNICAL FIELD

The present invention relates to a diamond coated tool, and particularlyto a diamond coated tool in which a base material has a surface coatedwith a diamond layer.

BACKGROUND ART

A diamond coated tool having a structure in which a material such ascemented carbide serves as a base material and the base material has asurface coated with a polycrystalline diamond layer, has been developedsince long ago.

A diamond coated tool in which a base material has a surface coated witha diamond layer has a rigid surface, and is therefore capable ofprocessing difficult-to-cut materials, such as fiber reinforced plastics(FRP) and the like, which have been considered to be difficult toprocess with a tool.

In applying a diamond coated tool to the difficult-to-cut materialsdescribed above, one of the determinants of the tool's life is adhesionbetween a base material and a diamond layer. That is, a diamond coatedtool has a problem of being prone to exfoliation randomly occurring incutting at an interface between a base material and a diamond layer,which results in a degraded grade of a cut material processed with acutting tool after exfoliation and an unstable cutting tool life.

It has been conventionally attempted to increase adhesion between a basematerial and a diamond layer. For example, Japanese Patent Laying-OpenNo. 04-263075 (hereinafter referred to as “Patent Document 1”) proposesa diamond coated tool in which a base material having a surface on whichfine asperities are formed is used and a diamond layer is formed on thebase material.

As shown in Patent Document 1, by forming a diamond layer on a basematerial having a surface with asperities, an anchor effect occursbetween the base material and the diamond layer. This anchor effect canincrease adhesion between the base material and the diamond layer. Sucha diamond coated tool is resistant to exfoliation in the early stage ofcutting between the base material and the diamond layer.

The diamond coated tool of Patent Document 1, however, experiences highfrequency of exfoliation at an interface between the base material andthe diamond layer when cutting is continued for a long time, and theproblem of exfoliation between the base material and the diamond layerhas not been fully solved. Further, Japanese Patent Laying-Open No.2002-079406 (hereinafter referred to as “Patent Document 2”) alsodiscloses a technology to form asperities on a surface of a basematerial, as in Patent Document 1. The technology, however, does notshow any remarkable improvement in prolongation of the life of a diamondcoated tool.

Meanwhile, exfoliation between a base material and a diamond layer isbelieved to be caused by a difference between a coefficient of thermalexpansion of the base material and a coefficient of thermal expansion ofthe diamond layer. That is, it is presumed that when a diamond coatedtool reaches high temperatures due to heat in cutting, compressive ortensile residual stress is exerted on a diamond layer in the vicinity ofan interface with the base material, thereby causing exfoliation tooccur between the base material and the diamond layer.

For this reason, Japanese Patent Laying-Open No. 11-058106 (hereinafterreferred to as “Patent Document 3”) takes an approach of relaxingresidual stress occurring in a diamond layer when a diamond coated toolreaches high temperatures to achieve increased adhesion between a basematerial and the diamond layer. Specifically, adhesion between a basematerial and a diamond layer is increased by controlling the coefficientof thermal expansion and a material of a base material, the thickness ofa diamond layer, and the like.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Japanese Patent Laying-Open No. 04-263075-   Patent Document 2: Japanese Patent Laying-Open No. 2002-079406-   Patent Document 3: Japanese Patent Laying-Open No. 11-058106

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Adhesion between a base material and a diamond layer tends to beincreased by the technology disclosed in Patent Document 3. Thetechnique of Patent Document 3, however, extremely limits the materialof a base material, the thickness of a diamond layer, and the like. Thisoften leads to a design which ignores manufacturing cost, and thetechnology has hardly reached practical use.

In recent years, materials subjected to cutting are on a trend ofincreasingly becoming difficult to cut, and the progress of technologyof processing cutting tool is rapid. Therefore, the quality required fora diamond coated tool is also increasingly becoming higher.

For the diamond coated tool, a number of technologies for enhancingadhesion between a base material and a diamond layer have been proposedas described above. However, the adhesion cannot be yet said to besufficient, and further enhancement of adhesion is desired.

The present invention has been made in view of the circumstances asdescribed above, and an object of the invention is to provide a diamondcoated tool which is resistant to exfoliation at an interface between abase material and a diamond layer, not only in the early stage ofcutting but also when cutting is continued for a long time.

Means for Solving the Problems

The diamond coated tool of the present invention is a diamond coatedtool including a base material and a diamond layer coating a surface ofthe base material, and characterized in that the surface of the basematerial has an arithmetic average roughness Ra of not less than 0.1 μmand not more than 10 μm and an average length of roughness profileelements RSm of not less than 1 μm and not more than 100 μm, and thatthe diamond layer has a plurality of cavities extending from a portionbordering on the base material in a crystal growth direction.

Preferably, arithmetic average roughness Ra is not less than 0.4 μm andnot more than 4 μm, and average length of roughness profile elements RSmis not less than 2 μm and not more than 20 μm.

Preferably, in a given section taken through the diamond coated tool ata plane including the base material and the diamond layer, the number ofcavities relative to the length of the base material is not less than1×10³/cm and not more than 1×10⁶/cm.

Preferably, the cavities have a width of not less than 5 nm and not morethan 200 nm relative to the crystal growth direction and a length of notless than 10 nm and not more than 1 μm in the crystal growth direction.Preferably, the diamond layer is made of polycrystalline diamond.Preferably, the diamond layer is formed by chemical vapor depositionprocess.

The diamond coated tool of the present invention as above can besuitably used to cut difficult-to-cut materials.

Effects of the Invention

With a configuration as described above, the diamond coated tool of thepresent invention achieves increased resistance to exfoliation between abase material and a diamond layer and an improved tool life, even whencutting is performed continuously with the tool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of the diamond coated tool ofthe present invention in the vicinity of an interface between a basematerial and a diamond layer.

FIG. 2 shows a graphed cross-section of a base material used for thediamond coated tool of the present invention with an indication ofarithmetic average roughness Ra.

FIG. 3 shows a graphed cross-section of a base material used for thediamond coated tool of the present invention with an indication of thelength of contour curve element Xs.

FIG. 4 is a photographed image taken in a transmission electronmicroscopic observation of a cross-section of the diamond coated tool ofthe present invention.

MODES FOR CARRYING OUT THE INVENTION

The present invention will be described below in more detail.

Diamond Coated Tool

FIG. 1 is a schematic cross-sectional view of the diamond coated tool ofthe present invention in the vicinity of an interface between a basematerial and a diamond layer. A diamond coated tool 10 of the presentinvention includes a base material 1 and a diamond layer 3 formed onbase material 1, as shown in FIG. 1. Diamond coated tool 10 of thepresent invention with such a configuration can be extremely useful as adrill, an end mill, a blade-edge-replaceable cutting tip for milling orlathe turning, a metal saw, a gear cutting tool, a reamer, a tap, or atip for pin milling of a crankshaft, a cutting piece for cutting ofglass-substrate, an optical fiber cutter, for example.

As seen from the above, the diamond coated tool of the present inventioncan be used for various applications, and in particular, it can besuitably used for processing difficult-to-cut materials which areconsidered to be difficult to process with conventional cutting tool.That is, the diamond coated tool of the present invention can beextremely effectively used for processing difficult-to-cut materials,since it has a surface to which enhanced hardness is imparted ascompared with that of conventional cutting tools.

Base Material

As base material 1 of diamond coated tool 10 of the present invention,any conventionally known base material which is known as a base materialfor such cutting can be used without any particular limitation. Examplesof such base materials can include: cemented carbide (for example, WCbased cemented carbide, including those containing Co in addition to WCand possibly further having an additive of carbonitride or the like,such as Ti, Ta or Nb), cermet (those consisting primarily of TiC, TiN,TiCN or the like), high-speed steel, tool steel, ceramic (for example,titanium carbide, silicon carbide, silicon nitride, aluminum nitride,aluminum oxide, and a mixture thereof), cubic boron nitride sinteredbody, diamond sintered body, and the like.

When cemented carbide is used as a base material, even if the structureof such cemented carbide includes a free carbon and an abnormal phasecalled η-phase, the effects of the present invention are exhibited.

It is noted that base material 1 used in the present invention may aswell have a modified surface. For example, in the case of cementedcarbide, a β-free layer may be formed at a surface thereof, and in thecase of cermet, a surface-hardened layer may be formed. Even with such amodified surface, the effects of the present invention are exhibited.

The present invention is characterized in that base material 1 having asurface shaped with asperities is used. Such an asperity shape has amean value of amplitudes of asperities in the direction of height and amean value of lateral amplitudes of asperities, which are each definedat a predetermined value. Specifically, a mean value of amplitudes ofasperities in the direction of height is defined as an arithmeticaverage roughness Ra, which is required to be not less than 0.1 μm andnot more than 10 μm. Further, a mean value of lateral amplitudes ofasperities is defined as an average length of roughness profile elementsRSm, which is required to be not less than 1 μm and not more than 100μm.

Here, taking FIG. 2 described below for example, arithmetic averageroughness Ra means a mean value of y-axial variations of a roughnessprofile (y=Z(x)) relative to a reference line (y=0). On the other hand,taking FIG. 3 described below for example, given that a point at whichroughness profile y=Z (x) changes from positive to negative is areference point, average length of roughness profile elements RSm meansan average of a length from one reference point to another adjacentreference point. It is noted that Ra and RSm will be described later indetail in conjunction with FIGS. 2 and 3.

Allowing Ra and RSm of a surface roughness of a base material to fallwithin a predetermined numerical range in this manner facilitatesanchoring of an early development core of a diamond into the basematerial in the formation of a diamond layer described later, andtherefore, increased adhesion between the base material and the diamondlayer can be achieved.

Furthermore, by coating a base material having a specific asperity stateas described above with a diamond layer by a chemical vapor deposition(CVD) process, a plurality of cavities 2 which extend from a portionbordering on base material 1 in a crystal growth direction can be formedin diamond layer 3, as shown in FIG. 1. These cavities 2 then exhibit afunction of relaxing residual stress produced at diamond layer 3 due toa difference between coefficients of thermal expansion of base material1 and diamond layer 3.

The relaxing effect exerted by cavities 2 on residual stress, combinedwith the above-described anchor effect, can remarkably enhance adhesionbetween base material 1 and diamond layer 3. Their synergistic effectprovides the present invention with resistance to exfoliation at aninterface between base material 1 and diamond layer 3 even if cutting isperformed continuously. It is noted that details of cavities 2 will bedescribed later.

Here, preferably, the above-described Ra is not less than 0.4 μm and notmore than 4 μm, and RSm is not less than 2 μm and not more than 20 μm.More preferably, Ra is not less than 1.3 μm and not more than 2.6 μm,and RSm is not less than 3 μm and not more than 6 μm. By imparting suchsurface roughness to a base material, in addition to the above-describedenhancing effect on adhesion between a base material and a diamondlayer, a smooth surface of a tool after deposition of a diamond layercan be achieved. Moreover, adhesion of diamond layer to a base materialcan be increased, and therefore, improved processing grade of a materialsubjected to cutting and prolonged tool life can be both achieved.

Examples of methods for forming asperity state as described aboveinclude a chemical etching treatment, a sandblasting treatment, anelectrochemical etching treatment, a combination of these treatments,and the like.

Here, each of the above-indicated etching processes will be illustratedby a specific example. An example of a chemical etching treatmentincludes immersing a base material in a mixed acid of sulfuric acid andacetic acid to dissolve a part of a surface of the base material.Preferably, a mixed acid used for a chemical etching treatment has asulfuric acid concentration of not less than 10% by mass and not morethan 98% by mass and an acetic acid concentration of not less than 10%by mass and not more than 70% by mass. Further, preferably, the timeduration of immersion of a base material in a mixed acid is not lessthan 30 seconds and not more than 60 minutes.

An example of a sandblasting treatment includes blasting particles ofalumina and silicon carbide. Preferably, particles used for asandblasting treatment have a mean particle size (diameter of aparticle) of not less than 5 μm and not more than 80 μm. Preferably,blast injection pressure of the particles against a base material is notless than 0.1 MPa and not more than 0.4 MPa. An example of anelectrochemical etching treatment includes electrolyzing Co contained incomponents of a base material, in electrochemical manner.

Arithmetic Average Roughness

What is called arithmetic average roughness Ra in the present inventionis a parameter indicating the length of asperities in the direction ofheight that are formed on a surface of a base material. The larger valueof Ra indicates the rougher irregularity of asperities. A method ofdetermining arithmetic average roughness Ra by calculation will bedescribed below using FIG. 2. FIG. 2 shows a graphed exemplarycross-section of a base material used for the present invention. Asshown in FIG. 2, a function of roughness profile of a base material in areference length L is expressed by y=Z(x). Here, a reference line (aline shown by y=0) of a roughness profile (y=Z(x)) is defined such thatwith regard to the area of portions enclosed by the reference line andthe roughness profile, the sum total area of portions located below thereference line and the sum total area of portions located above thereference line are equal. That is, in FIG. 2, the roughness profilelocated below the reference line is folded up above the reference line,and a dashed line shows an outline of the folded portion. The referenceline (y=0) is defined such that the sum total area of a diagonallyshaded portion enclosed by the dashed line and the sum total area ofdiagonally shaded portion enclosed by a solid line of the roughnessprofile are equal. Mathematically, the reference line is defined tosatisfy Expression (1) below.∫₀ ^(L) Z(x)dx=0  (1)

Arithmetic average roughness Ra in the present invention is determinedwith reference to the reference line defined in the above-describedmanner, by calculation integrating an absolute value of the roughnessprofile with respect to reference length L (i.e., integrating a functionof y=|Z(x)| in the range of 0≦x≦L) and dividing the obtained value by L.That is, arithmetic average roughness Ra is determined by calculation ofExpression (2) below.

$\begin{matrix}{{Ra} = {\frac{1}{L}{\int_{0}^{L}{{{Z(x)}}\ {\mathbb{d}x}}}}} & (2)\end{matrix}$

To conceptually describe arithmetic average roughness Ra using FIG. 2,the height given by averaging the above-described sum of the area ofdiagonally shaded portions enclosed by the dashed line and the area ofdiagonally shaded portions enclosed by the solid line of the roughnessprofile, by reference length L, corresponds to arithmetic averageroughness Ra.

Average Length of Roughness Profile Elements

Average length of roughness profile elements RSm in the presentinvention is a parameter indicating a widthwise length of an asperitystate formed on a surface of a base material (pitch). The larger valueof RSm indicates the lower pitch of asperities. In the presentinvention, average length of roughness profile elements RSm employs amethod specified in JIS B0601:2001. Based on FIG. 3, a method ofdetermining average length of roughness profile elements RSm bycalculation is now described. FIG. 3 shows a graphed cross-section of abase material used for the present invention. In FIG. 3, when the lengthfrom a point at which the roughness profile (y=Z(x)) switches frompositive to negative (hereinafter referred to “reference point”) toanother adjacent reference point is defined as a length of contour curveelements Xs, m lengths of contour curve elements (Xs1, Xs2, Xs3 . . .Xsi . . . . Xsm in FIG. 3) can be obtained in the range of referencelength L. The mean value of these m lengths of contour curve elements isaverage length of roughness profile elements RSm. That is, averagelength of roughness profile elements RSm is determined by calculation ofExpression (3) below.

$\begin{matrix}{{RSm} = {\frac{1}{m}{\sum\limits_{i = 1}^{m}\;{Xsi}}}} & (3)\end{matrix}$

It is noted that, as clearly seen from FIG. 3, the total sum of mlengths of contour curve elements Xs1, Xs2, Xs3 . . . Xsi . . . . Xsmcorresponds to reference length L. Therefore, average length ofroughness profile elements RSm in Expression (3) can also be simplyexpressed as L/m.

Method of Measuring Surface Roughness

As to the above-described parameters of surface roughness (Ra and RSm),a surface of a base material may be measured prior to the formation of adiamond layer on the base material, or a surface of a base material maybe directly or indirectly measured after the formation of a diamondlayer. It is, however, preferable to measure the surface roughness of abase material prior to the formation of a diamond layer on the basematerial in view of the fact that the surface roughness of the basematerial can be measured without causing any damage to the diamondlayer.

Here, as to a method of measuring the surface roughness of a basematerial, a device capable of parametric analysis in conformity with ISOstandards or JIS standards can be utilized. For example, a contactstylus measuring device and an optical (laser, interference, or thelike) measuring device are commercially available, and in particular, alaser microscope is suitable for measuring the surface roughness of thebase material of the present invention, because of a high spatialresolution and easy numerical analysis. Ra and RSm in the presentspecification are values obtained by a measurement using a lasermicroscope having a laser wavelength of 408 nm, a horizontal spatialresolution of 120 nm, and a vertical resolution of 10 nm.

Further, as a method of measuring the surface roughness of a basematerial after formation of a diamond layer on the base material, inaddition to a method by which a diamond layer is removed in any mannerfollowed by a measurement in the manner as illustrated above, one mayuse a method by which a base material is cut together with a diamondlayer, then, from a direction perpendicular to the section, asperitieson a surface are observed, and the observed asperities are quantified.

Even when a measurement of the surface roughness (Ra and RSm) of thebase material using measuring devices as illustrated above providesmeasurements that vary within the surface, if at least one point fallswithin the numerical range defined in the present invention, then theeffects of the present invention are exhibited. Here, it is preferablethat the surface roughness of a base material when reference L is set tobe not less than 10 μm satisfies the above-indicated numerical range.

Diamond Layer

In the present invention, preferably, a diamond layer formed on a basematerial is a film made of polycrystalline diamond. Here,polycrystalline diamond refers to diamond microparticles of on the orderof 10 nm to several μm which are firmly coupled together. Morepreferably, such a diamond layer is formed by a deposition process whichincreases crystallinity. Further, from the standpoint of forming aplurality of cavities extending from a base material in a crystal growthdirection concurrently with the formation of a diamond layer, it isnecessary to use a CVD process.

It is noted that in the present invention, the term “crystal growthdirection” refers to a vector direction in which, given a particularpoint on a surface of a base material as a base point, the shortestdistance from the base point to a surface of a diamond layer isobtained.

As a CVD process suitably used in forming a diamond layer, anyconventionally known CVD processes can be used without any particularlimitation. Examples of such CVD processes can include a microwaveplasma CVD process, a hot-filament CVD process, a plasma jet CVDprocess, and the like. In particular, it is preferable to employ a heatfilament CVD process.

Further, although it is preferable that the diamond layer of the presentinvention is formed such that the whole surface of a base material iscoated, the base material may have a portion not coated with the diamondlayer, and the diamond layer may have different composition at anyportion above the base material. Further, in the present specification,only the case in which a diamond layer is formed on a base material isdescribed, however, a single or more than one layer which is differentfrom the diamond layer may be formed between the base material and thediamond layer.

It is noted that the above-described diamond layer may include a foreignatom, such as boron, nitrogen, silicon, for example, and may include anincidental impurity other than these elements.

Cavities in Diamond Layer

The diamond coated tool of the present invention is characterized inthat when a diamond layer is formed on a base material, a plurality ofcavities extending from the base material in a crystal growth directionare formed in the diamond layer. Since the diamond layer has a pluralityof cavities, these cavities relax residual stress produced in thediamond layer due to a difference between coefficients of thermalexpansion of the base material and the diamond layer. This caneffectively prevent exfoliation between the base material and thediamond layer.

The above-described cavities can be confirmed with a scanning electronmicroscope (SEM). When the cavities are observed with SEM, the diamondcoated tool, including the diamond layer, is cut together with the basematerial, and a commercially-available device for preparing across-sectional sample is used for the section to prepare a sample forSEM observation. Then, the presence or absence of a cavity and the shapethereof can be ascertained by observing the sample in the vicinity of aninterface between the base material and the diamond layer by means of aSEM in an enlarged view.

It is noted that the above-described presence or absence of a cavity andthe shape thereof may be observed with a transmission electronmicroscope (TEM). When observing cavities with a TEM, a thin sectionincluding the base material and the diamond layer is created with afocused ion beam etching device, and the thin section is observed with aTEM.

In the present invention, preferably, in a given section taken throughthe diamond coated tool, the number of cavities relative to the lengthof the base material in the section is not less than 1×10³/cm and notmore than 1×10⁶/cm. By providing cavities in the diamond layer at such aratio, the relaxing effect by the cavities on the above-describedelastic stress can be increased.

The term “length of a base material” here refers to the length of aninterface between the base material and the diamond layer which appearsat a section taken through the diamond coated tool.

Further, preferably, the cavities are sized to have a width of not lessthan 5 nm and not more than 200 nm relative to the crystal growthdirection and a length of not less than 10 nm and not more than 1 μm inthe crystal growth direction. If the above-described cavities have awidth of less than 5 nm or a height of less than 10 nm, then the size ofcavities are not sufficient to obtain sufficient relaxing effect onresidual stress produced in the diamond layer. Further, if the cavitieshave a width of more than 200 nm or a length of more than 1 μm, thecavities are so large that the diamond layer is prone to a crackstarting from the cavity. In the present invention, it is not necessaryfor all cavities to fall within the above-described numerical range ofthe size, and it is only necessary for cavities appearing in a sectiontaken through a diamond layer together with the base material to includeone or more cavities falling within the above-described numerical range.

Here, the term the “width relative to the crystal growth direction”refers to a length in a direction orthogonal to the crystal growthdirection.

Furthermore, the size (width and length) of cavities in the diamondlayer can be ascertained by observing a given section taken through thediamond coated tool with the aforementioned SEM or TEM.

According to the study by the inventors of the present invention, it hasbeen found that the number and size of the cavities formed in thediamond layer are profoundly affected by the asperity state on a surfaceof the base material (i.e., numerical values of Ra and RSm). This is,however, not the only finding and it has also been found that gaspressure and gas composition in the formation of the diamond layer, aswell as the surface temperature of the base material and the like alsohave effect. Therefore, the desired number of cavities in the desiredsize can be formed by regulating the asperity state on a surface of thebase material and controlling various conditions in the formation of thediamond layer.

For example, when forming the diamond layer using a hot-filament CVDdevice, it is preferable that the gas pressure within the hot-filamentCVD device be not less than 1.3×10² Pa and not more than 2.6×10⁴ Pa.This allows for formation of the desired number of cavities in thedesired size. Further, as to composition of gas to be introduced, forexample, it is preferable to use a mixed gas or the like having a CH₄gas concentration relative to H₂ gas of not less than 0.3% by volume andnot more than 20% by volume. Further, preferably, the surfacetemperature of the base material in the formation of the diamond layeris not less than 600° C. and not more than 1100° C.

EXAMPLES

The present invention will be described below in more detail withexamples to which the present invention is not limited.

It is noted that although the diamond layer is hereinafter formed by ahot-filament CVD process, the diamond layer may be formed by aconventionally known CVD process, for example, a microwave plasma CVDprocess, a plasma jet CVD process, and the like.

Examples 1-14 and Comparative Examples 1-9

In the fabrication of diamond coated tools of examples and comparativeexamples, a base material made of HS K10 cemented carbide (WC-5% Co) andhaving a tool shape of SNMN120412 was used as the base material of thediamond coated tools.

The surface of the above-described base material was then etched byimmersing the surface of the base material in a mixed acid of 98% bymass sulfuric acid and 60% by mass acetic acid for 20 minutes. Then, asandblasting treatment was performed by which media having a variety ofparticle sizes (particles having a mean particle size of between 5 μmand 50 μm) was blasted against the base material at a blast injectionpressure of 0.3 MPa. The base materials after the sandblasting treatmentand to be used for examples and comparative examples were measured withrespect to parameters Ra and RSm of their surface roughness using anoptical laser microscope (product name: LEXT OLS3500 (manufactured byOlympus Corporation)). The result is shown in Table 1 below.

Next, a treatment for seeding nanosized diamond powder on the surface ofthe base material was performed. The base material which had receivedseeding treatment as above was then set in a publicly known hot-filamentCVD device. In examples and comparative examples (except for Example 14and Comparative Example 5), then 1% CH₄/H₂ gas was introduced into thehot-filament CVD device, its inner pressure was set at 4.0×10³ Pa, andby means of a temperature adjustment device including a coolingmechanism which was installed in the hot-filament CVD device, thetemperature of the above-described surface of the base material was setat 900° C. and the temperature of the filament was set at 2050° C. Adiamond layer was then formed on the base material by a 10-hour growthunder the diamond growth conditions described above. In this way, thediamond coated tools of examples and comparative examples (except forExample 14 and Comparative Example 5) were fabricated. A Ramanspectroscopic examination of the diamond layers of the diamond coatedtools fabricated in this way reveled that their structures were allpolycrystalline diamond.

FIG. 4 is a photographed image taken in a transmission electronmicroscopic observation of a section taken at a given plane of thediamond coated tool fabricated in Example 1. As clearly seen from FIG.4, it is understood that diamond layer 3 which has a plurality ofcavities 2 extending from the base material in a crystal growthdirection is formed by forming, under specified manufacturingconditions, diamond layer 3 on base material 1 having the parameters ofthe surface roughness (Ra and RSm) falling within a predeterminednumerical value range.

Based on the photographed image of the section of FIG. 4, the number ofcavities 2 relative to the length of base material 1 was determined bycalculation. The result was that at a given plane of the section of thediamond coated tool, base material 1 had a length of 3 μm, and threecavities 2 were present for this length of base material 1. Accordingly,the number of cavities relative to the length of the base material wasdetermined by calculation as 3/3 μm=1.0×10⁴/cm.

Further, the size of a specific cavity of the cavities presented in thephotographed image of the section of FIG. 4 was determined bycalculation. The cavity size was a width of 20 nm relative to thecrystal growth direction and a length of 500 nm in the crystal growthdirection.

As to the diamond coated tools of Examples 2-13 and Comparative Examples1-4 and 6-9, the number and size of cavities were also determined bycalculation in the same manner as Example 1 described above. The resultsare shown in Table 1 below.

TABLE 1 Surface Cavity Roughness Number of Cavity/ Ra RSm Length of BaseMaterial Size (nm) (μm) (μm) (number/cm) Width Length Example 1 2.5 5.21.0 × 10⁴ 20 500 Example 2 0.42 2.1 1.1 × 10⁵ 10 100 Example 3 3.8 195.5 × 10³ 100 720 Example 4 0.11 1.1 1.0 × 10⁶ 5 10 Example 5 9.8 99 1.0× 10³ 200 1000 Example 6 0.41 18 2.3 × 10⁵ 8 95 Example 7 3.9 2.2 6.9 ×10³ 95 680 Example 8 0.12 98 9.2 × 10⁵ 6 15 Example 9 9.9 1.2 3.1 × 10³150 880 Example 10 0.25 9.8 3.3 × 10⁵ 6 15 Example 11 1.3 31 2.5 × 10⁴18 420 Example 12 5.6 5.9 4.1 × 10³ 120 710 Example 13 1.9 1.5 1.9 × 10⁴19 430 Example 14 1.9 2.3 1.0 × 10⁶ 5 10 Comparative Example 1 0.09 0.92.0 × 10⁶ 4 9 Comparative Example 2 11 103 9.5 × 10² 250 1500Comparative Example 3 0.09 105 1.5 × 10⁵ 3 8 Comparative Example 4 110.95 9.1 × 10² 220 1200 Comparative Example 5 2.4 5.1 N/A ComparativeExample 6 1.8 108 9.8 × 10³ 6 9 Comparative Example 7 3.1 0.96 9.1 × 10³4 20 Comparative Example 8 0.08 4.9 2.6 × 10⁵ 4 8 Comparative Example 910.5 7.5 1.1 × 10³ 6 8

It is noted that in Examples 1-13 and Comparative Examples 1-4 and 6-9,the base materials with different surface roughness from each other wereused, and consequently, even though the diamond layers were fabricatedin the same manner, the number and size of the cavities formed in thediamond layers were different from each other.

Meanwhile, in Example 14 and in Comparative Example 5, the diamondlayers were deposited under conditions different from those of theabove-described examples. Specifically, in Example 14, gas pressure andgas composition were altered from manufacturing conditions of theabove-described examples to regulate the size and number of cavitiesformed in the diamond layer as shown in Table 1. In Comparative Example5, the diamond layer was formed while regulating gas pressure and gascomposition so as not to form cavities in the diamond layer.

The diamond coated tool of each example fabricated in this way is adiamond coated tool including a base material and a diamond layercoating a surface of the base material, the surface of the base materialhaving arithmetic average roughness Ra of not less than 0.1 μm and notmore than 10 μm and average length of roughness profile elements RSm ofnot less than 1 μm and not more than 100 μm, and the diamond layerhaving a plurality of cavities extending from the base material in acrystal growth direction.

Evaluation of Adhesion of Diamond Coated Tool

The diamond coated tools of Examples 1-14 and Comparative Examples 1-9fabricated in the above were respectively evaluated as to adhesion bybeing subjected to wet intermittent cutting. Cutting conditions were asshown in Table 2 below. A round bar of an Al-16% Si raw material whichwas provided with six grooves was used as the material subjected tocutting. Cutting was performed under conditions of a cutting rate of 400m/min, a cutting depth of 0.5 nm, and a feed rate of 0.12 mm/rev. Toevaluate adhesion under these cutting conditions, cutting was stopped atregular time intervals to observe the state of a blade edge, and theduration of time before the diamond layer exfoliates was employed as anevaluation index.

TABLE 2 Cutting Conditions Material subjected to Round bar of Al-16% Sicutting having six axial grooves Cutting Rate 400 (m/min) Feed Rate 0.12(mm/rev) Cutting Depth 0.5 (mm)

As a result of the above-described evaluation of adhesion, the timeduration before the diamond layers of examples and comparative examplesexfoliate was obtained, which are shown in Table 3 below. The longertime duration before exfoliation indicates the superior adhesion betweenthe base material and the diamond layer.

TABLE 3 Time Before Exfoliation of Diamond Layer (min) Example 1 100Example 2 85 Example 3 71 Example 4 69 Example 5 61 Example 6 77 Example7 73 Example 8 68 Example 9 63 Example 10 70 Example 11 72 Example 12 71Example 13 69 Example 14 95 Comparative Example 1 11 Comparative Example2 9 Comparative Example 3 12 Comparative Example 4 6 Comparative Example5 2 Comparative Example 6 16 Comparative Example 7 13 ComparativeExample 8 14 Comparative Example 9 15

As clearly seen from Table 3, it is apparent that the diamond coatedtools of Examples 1-14 according to the present invention have enhancedadhesion as compared with the diamond coated tools of ComparativeExamples 1-9. It has been confirmed that the life of the diamond coatedtools has been improved.

Although embodiments and examples of the present invention have beendescribed as above, it is also contemplated from the beginning tosuitably combine configurations of the above-described embodiments andexamples.

It should be construed that the embodiments and examples disclosedherein are by way of illustration in all respects, not by way oflimitation. It is intended that the scope of the present invention isdefined by claims, not by the above description, and includes allmodifications equivalent in meaning and scope to the claims.

DESCRIPTION OF THE REFERENCE SIGNS

1 base material, 2 cavity, 3 diamond layer, 10 diamond coated tool.

The invention claimed is:
 1. A diamond coated tool comprising: a basematerial; and a diamond layer coating a surface of said base material,the surface of said base material having an arithmetic average roughnessRa of not less than 0.1 μm and not more than 10 μm and an average lengthof roughness profile elements RSm of not less than 1 μm and not morethan 100 μm, said diamond layer having a plurality of cavities extendingfrom a portion bordering on said base material in a crystal growthdirection, wherein in a given section taken through said diamond coatedtool at a plane including said base material and said diamond layer, thenumber of said cavities relative to a length of said base material isnot less than 1×10³/cm and not more than 1×10⁶/cm, and wherein saidcavities have a width of not less than 5 nm and not more than 200 nmrelative to the crystal growth direction and a length of not less than10 nm and not more than 1 μm in the crystal growth direction.
 2. Thediamond coated tool according to claim 1, wherein said diamond layer ismade of polycrystalline diamond.
 3. The diamond coated tool according toclaim 1, wherein said diamond layer is formed by chemical vapordeposition process.